aws: dual-stack enabled by default with no way to disable

PR https://github.com/hashicorp/go-discover/pull/271 introduced dual-stack configuration for AWS and enables this by default. While this is fine, there is no way to disable dual-stack behaviour. This issue therefore requests a configuration option or way to disable dual-stack; an environment variable for example would be great.

Nomad related issue: https://github.com/hashicorp/nomad/issues/26233